1. Field of the Invention
The present invention relates to a water-cooled type engine cooling apparatus, and also relates to a transmission oil cooler module for regulating the temperature of hydraulic oil for a transmission to a preset temperature due to heat exchange with the water temperature of cooling water flowing out of a water-cooled type engine.
2. Description of the Related Art
As a water-cooled type engine cooling apparatus, a technique disclosed in JP-UM-A-4-041972 (1992) is known in the related art. In the water-cooled type engine cooling apparatus disclosed in this official gazette, an oil cooler and an air conditioner are provided. The oil cooler heats and cools hydraulic oil for a transmission by use of cooling water for an engine. The air conditioner conditions the air in a cabin. Thus, even when the temperature of the hydraulic oil is low, for example, just after the start-up of the engine, the hydraulic oil is heated by the oil cooler so that proper viscosity can be secured in the hydraulic oil while friction loss in the automatic transmission can be reduced. Thus, fuel economy is improved in a vehicle.
However, the related art has problems as follows. That is, the hydraulic oil for the automatic transmission does not drop very much in spite of continuous stop of the engine in a season with a good climate such as spring or autumn. Further, when the air conditioner is used, the difference between target temperature to be set by a passenger and outdoor air temperature is so small that the fuel economy can be improved even if the air conditioner is operated while the hydraulic oil is heated by use of the cooling water. However, in an environment such as winter, in which the outdoor air temperature is very low, the hydraulic oil for the automatic transmission becomes very low in temperature due to continuous stop of the engine. Further, the difference between the target temperature and the outdoor air temperature increases. As a result, when heating of the hydraulic oil and heating of the air in the cabin are performed simultaneously, increase in the energy used for heating the hydraulic oil results in reduction in the heating performance of the air conditioner. Thus, there is a problem that it takes much time to attain the target temperature.
In addition, it is a well-known fact that when the engine is operated at a temperature as high as possible, the friction loss of the engine itself is reduced so that the fuel economy is improved. In order to accelerate warming-up of the engine when starting up from a cold state, control is typically made to increase fuel oil consumption at idling time till the temperature of the engine reaches predetermined temperature (hereinafter referred to as “warming-up control temperature”). Therefore, when heating of the hydraulic oil and heating of the air are performed together in the circumstances that the outdoor air temperature is low, there occurs a delay in increasing the temperature of the cooling water to the warming-up control temperature. Thus, there is a problem that the fuel economy is deteriorated.
In order solve these problems, there is provided a transmission oil cooler in which a bypath and a valve are provided in an oil circuit for circulating hydraulic oil for a transmission through the oil cooler so that the valve opens the bypath when the temperature of the hydraulic oil is not higher than predetermined temperature, and the valve closes the bypath when the temperature of the hydraulic oil exceeds the predetermined temperature, as disclosed in JP-A-6-272558 (1994). That is, when the oil temperature is not higher than the predetermined temperature, the hydraulic oil is made to bypass the oil cooler through the bypath so as to avoid heat exchange with the cooling water and thereby accelerate the increase of the water temperature. Thus, the air conditioner is prevented from being degraded in its heating performance. When the oil temperature exceeds the predetermined temperature, the bypath is closed so that heat exchange between the hydraulic oil and the cooling water is carried out to increase the temperature of the hydraulic oil. Thus, the friction loss of the automatic transmission is reduced.
However, in the transmission oil cooler, avoidance and execution of heat exchange between the hydraulic oil and the cooling water are controlled in accordance with the temperature of the hydraulic oil. Thus, there is a problem that even when the cooling water temperature is lower than the warming-up control temperature, the heat exchange between the hydraulic oil and the cooling water is executed so that the temperature of the cooling water is prevented from increasing. Further, in the known example, cutting is required for the casing that forms the outer circumference of the valve. In addition, work of bolting or the like is also required for installing the oil cooler. Thus, there is a problem that it takes much labor for installation so that the cost is increased.